Controlled gradient compression leaf spring



Nov. 27, 1956 E. E. FOSTER CONTROLLED GRADIENT COMPRES\SION LEAF SPRING Filed llay 5. 154

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ATTORNEYS.

United States Patent CONTROLLED GRADIENT COMPRESSION LEAF SPRING Edwin E. Foster, Austin, Tex., assignor to Majik-Ironers, Inc., Austin, Tex., a corporation of Texas Application May 3, 1954, Serial No. 426,992

3 Claims. (Cl. 267-1) This invention relates to a controlled gradient compression leaf spring, and more particularly to a leaf spring which can produce a constant compression gradient or a negative pressure gradient over a wide range of movement.

The conventional compression spring of either the coil or leaf type has a positive and substantial linear gradient over its full range of movement. There are many applications where a positive gradient is undesirable and where it is necessary to provide either constant or negative gradients for the desired effects.

It is one of the objects of the present invention to provide a spring of the leaf type which is designed to produce a controlled gradient of the desired character over a wide range of movement.

Another object is to provide a leaf spring in which the spring strip or leaf is normally bowed in One direction and is bowed in the opposite direction by compressive forces on its ends.

According to one feature of the invention, the initial bowing of the strip can be controlled to produce either a constant pressure gradient or a negative gradient.

The above and other objects and features of the invention will be more readily apparent from the following description when read in connection with the accompanying drawing in which:

Figure 1 is an elevation of a leaf spring embodying the invention;

Figure 2 is a side view of the spring in its relaxed condition;

Figure 3 is a side view of the spring in its loaded position illustrating deflection thereof under load;

Figure 4 is a view similar to Figure 2 of an alternative construction for producing a negative gradient; and

Figure 5 is a view similar to Figure 3 of the spring of Figure 4.

The spring of the present invention as shown in Figures 1 to 3, is designed to produce a constant compression gradient over a wide range of movement illustrated as approximating one-half the length of the spring. The spring is formed of a strip of spring material, such as resilient metal, and is preferably cut to a diamond shape as shown in Figure l, with relatively narrow end portions and 11 which taper to a central portion 12 of maximum width.

For producing constant compression, the spring is bowed slightly in one direction opposite to the direction in which it is adapted to flex under load. As shown in Figure 2, the spring strip is bowed to be convex when viewed from the left with a relatively small degree of bow. When the spring is loaded the central portion 12 thereof is moved to the right past the plane of the ends of the spring to which the compressive load is applied as illustrated in full lines in Figure 3. An adjustable stop, as shown at 13, may be provided to hold the spring bowed to the right.

Depending upon the thickness and width and character of the spring material,-the spring when initially bowed to ice the small extent illustrated, will exert a compressive load which will remain substantially constant throughout full deflection of the spring. In the example shown, the spring may exert a force of 12. pounds in its initial position and will exert the same 12 pound force as it is compressed by compressive forces applied to its ends as indicated by the arrows 14 until it reaches its fully compressed position illustrated in dotted'lines. It will be understood that the only limitation on flexing of the spring is the elastic limit of the spring material, and that the spring can be compressed to any extent which will not stress the material beyond its elastic limit with a constant compressive force.

For some applications, it is desirable to provide a negative compression gradient and for this purpose, the spring may be constructed as shown in Figures 4 and 5. The spring leaf or strip may be identical with the strip shown in Figure 1 with its ends 15 arranged to receive the compressive load. In this case, however, the spring is initially bowed to a greater extent than with the constant compression spring of Figures 2 and 3 as will be apparent from a comparison of Figure 4 with Figure 2. When the spring is loaded it is bowed in the opposite direction as illustrated in Figure 5, and the load is applied to the ends thereof as shown by the arrows 16. When a spring of this type is initially pretensioned to a large extent, as shown in Figure 4, it has been found that the load required to compress the spring will decrease as the spring is compressed to produce a negative compression gradient. For example, the spring may exert an initial force of 12 pounds when it is initially loaded, as shown in full lines in Figure 5. As the spring is compressed to its maximum degree of compression shown in dotted lines in Figure 5, the compressive resistance thereof will decrease substantially linearly and may reach a value approximating half of the initial loading as indicated in Figure 5.

By varying the amount of initial tension in the direction opposite to the direction of bowing under load and by changing the physical size and the characteristics of the material substantially any desired gradient can be produced.

While two embodiments of the invention have been shown and described in detail, it will be apparent that these are illustrative only and are not to be taken as a definition of the scope of the invention, reference being had for this purpose to the appended claims.

What is claimed is:

l. A controlled gradient compression spring comprising a strip of spring material, ends on the strip through which a compressive load is applied to move the ends of the strip relatively toward each other, the strip being normally bowed in one direction in its relaxed condition, and means to hold the strip bowed in the opposite direction so that the strip will be bowed further in the opposite direction as its ends are moved toward each other in response to an applied compressive load.

2. A controlled gradient compression spring comprising a strip of spring material, ends on the strip through which a compressive load is applied to move the ends of the strip relatively toward each other, the strip being normally bowed in one direction in its relaxed condition, and means to hold the strip bowed in the opposite direction so that the strip will be bowed further in the opposite direction as its ends are moved toward each other in response to an applied compressive load, the bowing of the spring in said one direction being sufficient to produce a negative gradient when the spring is bowed in said other direction in response to the compressive load.

3. A controlled gradient compression spring comprising a strip of spring material, ends on the strip through which a compressive load is applied to move the ends of the strip relatively toward each other, the strip being normally bowed in one direction in its relaxed eonditidn, ahd 'means to hold the strip bowed in the opposite direction so that the strip will be bowed further in the opposite direction ,as its ends are mQved toward each other in IQ Mbrlrbski Sept. 15; 1942' V ..V 06f; =6, FOREIGN PATENTS 7 Germany Nov. 9, 1901 Great Britain Sept; 15, 1937 Great'Brit-a-in Feb.'25, 1942 V 

